1. Field of the Invention
The present invention relates to a blue-light emitting compound having fluorene side chains with superior emission efficiency, and a display device adopting the blue-light emitting compound as a color developing substance.
2. Description of the Related Art
Electroluminescence (EL) devices as a self-luminous type display give numerous advantages such as a broad viewing angle, a good contrast characteristic and a rapid response time. EL devices are classified into an inorganic EL device and an organic EL device depending on the material used for an emitter layer. In particular, the organic EL device has good luminance, turn-on voltage and response time characteristics and allows for full color display, compared to the inorganic EL device.
A general organic EL device includes an anode, a hole transporting layer, an emitter layer, an electron transporting layer and a cathode which are sequentially stacked on a substrate. The hole transporting layer, the emitter layer and the electron transporting layer are organic thin films formed of an organic compound.
The organic EL device having such a structure operates based on the following operational principle. As a voltage is applied between the anode and the cathode, holes injected from the anodes migrate through the hole transporting layer into the emitter layer. Meanwhile, electrons injected from the cathode migrate through the electron transporting layer into the emitter layer. In the emitter layer, excitons are generated by recombination of carriers, and transited from an excited state to ground state, so that fluorescent molecules of the emitter layer emit light, forming a picture.
An organic EL device adopting an aromatic diamine and aluminum complex having a low molecular weight has been developed by Eastman Kodak Company (Appl. Phys. Lett. 51, 913, 1987). Blue-light emitting substances, such as diphenylanthracene, tetraphenylbutadiene and distyryl benzene derivatives, have been disclosed, but their poor stability causes easy crystallization of thin films. EP 388,768 teaches diphenyldistyryl series blue-emitting materials with improved thin film stability, which hinders crystallization of thin film by adopting phenyl groups at its side chains. Also, distyrylanthracene derivatives, in which electron acceptors and electron donors coexist, have been developed by Kyushu University (Japan), which result in improved thin film stability (Pro. SPIE, 1910, 180 (1993)).
However, these blue light-emitting compounds lead to a reduction in the emission efficiency and need improvement of thin film stability, and thus a need for a novel blue-light emitting compound for blue-light emitting devices or full-color light-emitting devices, has increased.